This invention relates to the field of manufacturing carbon nanotubes, and more particularly, but not by way of limitation, to methods of manufacturing high-quality, single-walled carbon nanotubes.
Carbon exists in various molecular configurations, including diamond, graphite, fullerene, and carbon nanotube (CNT).
The CNT form of carbon was discovered relatively recently. Each CNT is a long, thin cylinder of carbon, with a diameter that can be as small as 1 nm and a length that can range from a few nanometers to one or more microns. A CNT may be thought of as a sheet of graphite, i.e., a hexagonal lattice of carbon, rolled into a cylinder.
A CNT may have a single cylindrical wall (SWCNT), or it may have multiple walls (MWCNT), giving it the appearance of cylinders inside other cylinders. A SWCNT has only a single atomic layer, whereas a MWCNT may contain, for example, from 100 to 1,000 atomic layers. Generally, SWCNTs are preferred over MWCNTs because they have fewer defects and are therefore stronger and more conductive than MWCNTs of similar diameter.
A CNT is considered to be the smallest known man-made structure that is self-supporting and chemically inert in the atmosphere. It may be conducting or semiconducting, depending on its diameter and helicity of arrangement (chirality) of graphite rings in its wall(s). The electrical conductivity of a CNT is roughly six times that of copper. Each CNT is as stiff as a diamond and exhibits extraordinary mechanical strength.
One of the most promising applications for CNTs is in nanotechnology, including the manufacture of reinforced composites and nano-electromechanical systems (NEMs). Briefly, nanotechnology science and engineering concerns the control of structures and devices at atomic, molecular, and supramolecular levels in order to create relatively large structures with a fundamentally new molecular organization. Many molecules may be used to make nanodevices and nanostructures, but the most promising and powerful because of their unique properties are the CNTs.
Several techniques exist for making CNTs, each requiring expensive equipment and/or the use of metal catalysts. For example, CNTs are currently manufactured in laboratories via laser ablation, electric-arc, or chemical vapor deposition (CVD) processes. Laser ablation and electric-arc techniques tend to (i) produce SWCNTs in small amounts (milligram to gram in a few hours) and (ii) employ metal catalysts. These catalysts may be difficult to completely remove from post-production CNTs, even after extensive cleaning and purification. Electric-arc techniques also require a closed or pressurized chamber, which can be costly and dangerous. There is also a CVD process used to grow nanotubes on patterned substrates, but it is more suitable for the development of nanoelectronic devices and sensors.
Another commonly used procedure is the HiPco process. The HiPco process has a good potential for large scale manufacturing of nanotubes. A major drawback of the HiPco process, however, is that it requires pressurized carbon monoxide, very high temperatures, and a metal catalyst that is difficult to remove at the end.
In short, there exists a need for a simple, low-cost method of manufacturing high-quality, single-walled carbon nanotubes that eliminates the need for extensive cleaning and purification of the CNT product.
It is an object of the present invention to provide a process of manufacturing carbon nanotubes.
It is another object of the present invention to provide a process of manufacturing single-walled carbon nanotubes.
It is a further object of the present invention to provide a simple, inexpensive process of manufacturing single-walled carbon nanotubes.
It is a still further object of the present invention to provide a metal catalyst-free process of manufacturing carbon nanotubes.
To achieve these objects of the invention, there is provided a process of manufacturing carbon nanotubes, comprising a step of inducing electrical current through a carbon anode and a carbon cathode under conditions effective to produce the carbon nanotubes, wherein the carbon cathode is larger than the carbon anode. Preferably, a welder is used to induce the electrical current via an arc welding process. Preferably, an exhaust hood is placed on the anode, and the process does not require a closed or pressurized chamber.
The present process is able to produce single-walled and multi-walled carbon nanotubes, while eliminating the need for (i) a metal catalyst and (ii) a closed or pressurized chamber. Consequently, the present process avoids the costly and potentially dangerous steps that have heretofore compromised other processes for manufacturing carbon nanotubes.